The subject matter of the present invention pertains to means for accessing a digital memory system.
In a conventional digital memory system, information is grouped into elements of words, bytes, and bits, with a word comprising one or more bytes and a byte comprising one or more, usually several bits. The elements are stored in a plurality of memory locations, with each location being identified by a unique memory address. Often the memory locations are divided logically into two sections spread across a like number of memory devices, with each section or device being identified further as odd or even depending upon the sense of a particular unit of each memory address. To access a particular memory location in such a conventional system, it is necessary merely to supply the system with signals representative of the appropriate memory address, and the function, i.e., read or write, to be performed. Once the particular location has been accessed, the information contained therein can be retrieved or updated as desired. Assuming a multi-byte memory word, it is possible with known prior art systems to access a memory device at both the byte level and the word level; that is, a memory access may be made to retrieve or update information defining any byte of a particular word as well as the entire word itself.
A problem arises when it is desired to retrieve or update a data element comprising bytes from more than one memory device, for example, a high-order byte from a first device and a low-order byte from a second device. Known prior art systems either do not permit such access or, if permitted, require that the information to be retrieved or updated be preprocessed or postprocessed outside the system in order to maintain the correct order of the bytes within the element.